N,N-dialkylaniline azo dyes, such as N,N-diethylaniline diazo aniline, may be used to tag petroleum fuels for purposes of taxi product identification, etc. Such dyes may be added to petroleum fuels, e.g., at between about 0.25 and about 100 parts per million by weight (ppm). Subsequently, the dyes may be identified by extraction with an acidic aqueous solution which produces a strong color.
To be useful as petroleum fuels markers, however, there are particular requirements for the form the dye should be in. Such dyes are solid and must be first of all be dissolved in a liquid, such as an aromatic solvent, which is compatible with the petroleum fuel.
Furthermore, extractable markers for tagging petroleum fuel are often packaged in conjunction with a non-extractable dye. Such dyes, include, for example, Automate Red B (Color Index: Solvent Red 164), Red NR (Color Index: Solvent Red 19), Red 1992, Blue 8 (Color Index: Solvent Blue 98), Blue 10, Orange 127, Blue-Black, etc.
Because regulatory agencies often have "intensity requirements" both for the extractable marker and for the non-extractable dye, it is desired to provide as concentrated solutions of such dyes as can be achieved. Also, when added to a non-extractable dyes, the solution of the extractable dye tends to increase the viscosity of the dye; thus, concentrated solutions are desired so that less solution need be added. Viscosity is particularly a problem in colder climates where the dye/marker solution may be stored in freezing conditions for extended periods of time.
The dyes used as markers in accordance with the invention are typically manufactured in a coupling reaction that produces a solid dye which is obtained as a filter cake, washed and dried. It has proven difficult to dissolve such dyes in fuel-compatible solvents and obtain highly concentrated solutions, 25 wt % dye solution being a typical upper limit. Furthermore, when dissolving such dyes, the solutions tend to have relatively high levels of insolubles, an undesirable characteristic of a fuel additive.
Accordingly, it is an object of the present invention to produce highly concentrated solutions of dialkylaniline dyes.